Required Practical 2: Cells

Question 1

How to calculate miotic index

Answer 1

Number of cells in mitosis/ total number of cells

(Within the field of view)

Question 2

True or false, miotic index is a percentage

Answer 2

False
It’s a decimal/ whole number
(It’s the proportion of cells in a tissue sample that are undergoing mitosis)

Question 3

…is the proportion of cells in a tissue sample that are undergoing mitosis

Answer 3

Miotic index

Question 4

3 main Steps for preparing and observing a root tip squash

Answer 4

1) Take 1cm of the root tip and soak in hydrochloric acid (This process is called fixing and stops any further cell division so cells going through mitosis will be frozen at their stage. It also breaks the middle Lamella (‘glue’ that holds different cells together so helps to separate the cells))

2) Add stain (Toluidine Blue) to the root tip which binds to the DNA to make the chromosomes visible

3) Produce a single layer of cells (so that light can pass through the specimen and you can see the individual cells) by placing a coverslip on top of the root tip and pressing firmly in the centre to squash the stained root tip

Question 5

A student prepared a stained squash of cells. Why did they only use the first 5mm of the root tip

Answer 5

It’s where mitosis occurs

Question 6

The part of the root tip where there are rapidly dividing cells is called the…meristem

Answer 6

Apical
(It’s at the very tip)

Question 7

When preparing a stained squash of onion root why did the student rest firmly on the cover slip

Answer 7

To produce a thin (single layer) of cells so that light can pass through, making the cells visible

Question 8

When preparing a stained squash of onion root why is a thin (single layer) of cells needed

Answer 8

So that light can pass through in order for the cells to be visible

Question 9

What stage of preparing the stained squash of onion tip ensures that light can pass through the cells so that the cells are visible

Answer 9

Firmly pressing down on the cover slip to create a thin (single) layer of cells

Question 10

Why is a stain used when investigating the stages of mitosis in a garlic root

Answer 10

So that the chromosomes are visible as the stain binds to DNA

Question 11

The first stage of preparing a stained root tip squash is to soak 1cm of root tip in…

Answer 11

Hydrochloric acid

Question 12

Why is the root tip soaked in hydrochloric acid before the cells can be examined under the microscope

Answer 12

It stops cell division so that cells going through mitosis are frozen at that stage so that the process (e.g prophase/ metaphase/ anaphase/ telophase etc) can be observed and it breaks the middle Lamella to help separate the cells